How can I erase partition that can't be modified?

I recently installed Linux mint along side mac os x using the option " install alongside Mac osx"... But now i want to install windows 7 with bootcamp, But it doesn't let me because of the partitions for linux mint. i tried deleting them but it says they can't be modified. do any of you how to delete those partitions without re installing osx? ( i have a lot of important files and some i can't get back without re purchasing)...😟